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| Dissertation / PhD Thesis/Book | PreJuSER-36128 |
1999
Forschungszentrum, Zentralbibliothek
Jülich
Please use a persistent id in citations: http://hdl.handle.net/2128/20512
Report No.: Juel-3687
Abstract: This work reports on the fabrication and characterization of ultrafast vertical metalsilicon- metal (IvISM) Schottky-barrier-photodiodos for the detection of visible and infrared light. The devices are manufactured on an epitaxial buried CoSi2 ground plate on silicon consisting of a high quality single crystalline silicon layer sandwiched between the buried CoSi2 layer and a top semitransparent metal layer. For wavelengths shorter than 1.1 JLIll, electron-hole pairs arc generated in the Si. They are separated by an internal electrical field and accelerated towards the metal electrodes. For shorter wavelengths, Si becomes transparent and carriers arc emitted from the internal semiconductor-metal interface. A photocurrent is produced. This so-called internal photoeffect is governed by different carrier dynamics: hot electrons or holes are injected from the metal layers into the silicon. Their· large excess energy leads to extremely fast electrical pulses. A new theoretical model for the hot carrier dynamics inside the detector is proposed and examined by detailed simulations. The resulting temporal response of the detectors was measured with a new setup, using a modelocked Ti:sapphire laser and an optical parametric oscillator, which generates ultrafast optical pulses (170 fs ) at IR wavelengths. At 820 nm the iVISI'1'! photodiodes show an impulse response as short as 3.5 ps FWHM for Si(100) and 6.7 ps FWHlvl for Si(l11). For the first time, the temporal response oflvISJ'1'1 photodiodes was investigated at 1250 and 1560 nm wavelengths with femtosecond resolution. MSM photodiodes with different top metallization (Cr, Ti and Pt) were analyzed. In addition, the dependence of the temporal response from the applied voltage, the temperature, the dispersion on the microstrip line and the area of the detector was studied. The experimental results were interpreted with respect to the model proposed. The Ti/Si/CoSi2 photodetectors showed an electrical pulse response of 3.2 ps F'~THlvI at 4 V bias. This is to our knowledge a record value. Furthermore, it is demonstrated that under certain conditions an even faster response can be achieved. At Hat band bias (no electrical field inside the detector) a very sharp pulse of 1.2 ps was observed. Other important characteristics of the diodes (e.g. Schottky-Barrier heights, dark current, quantum efficiency, respousivity, crystal quality of the layers) are presented.
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